The present invention relates generally to electrostatic discharge protection devices. More particularly, the invention relates to electrostatic discharge protection devices for connector-receptor assemblies where the electrostatic discharge protection device connects ground and core conductors to inhibit electrostatic charge accumulation when the connector-receptor are disconnected, and automatically disconnects this ground connection upon operative combination of the connector-receptor.
Electrostatic charge is a stationary electric charge which accumulates on various surfaces. An electrostatic discharge occurs when the electrostatic charge becomes substantial enough to overcome a dielectric material between the charge and another surface of a lower electrical potential. An example of such a discharge is naturally occurring lightning.
Electrostatic discharge in the realm of electronics can be devastating to microelectronic devices. A sharp voltage spike caused by an electrostatic discharge can cause permanent and costly damage to individual precision devices, such as random access memory (RAM) or other semiconductor devices, inter alia. Circuit designs which are specially susceptible to electrostatic discharge are those having external connections.
For example, a thicknet local area network (LAN) card in a personal computer is often designed with a BNC type connector extending to the exterior of the personal computer. A coaxial cable having a complimentary BNC connector is attached to the BNC connector on the card to provide access to a network. While the coaxial cable is unattached, electrostatic discharge can occur destroying the devices or components on the card without any physical manifestation leading to costly hardware diagnostics and subsequent repairs.
One solution to this problem has been to place a fixed shunting device on the connector until it is ready for use. The fixed shunting device would create a short circuit between the conductors in the connector, one of which is generally grounded, ensuring that electrostatic charge does not reach the internal electronics. A problem with this device is that it must be removed before the connector is mated with a receptor, id est, a complementary connector. Upon withdrawing the connector, the shunting device is often unavailable for re-insertion into the connector which again opens the electronic devices to possible damage.
A prior art electrical connector-receptor arrangement that provides for an automatic shorting of conductors upon disconnection and opening upon connection which does not require specifically configured receptacle surfaces is disclosed in U.S. Pat. No. 3,467,940 entitled "Electrical Connecting Spring Device", by W. H. Wallo, issued Sep. 16, 1969. This patent shows a coiled compression spring mounted in a separable plug and jack connector assembly wherein the spring automatically expands and grounds the plug in the absence of the jack. The spring is automatically compressed upon insertion of the jack into the plug and compressed so as to electrically disconnect from the plug. However, the coiled compression spring is shown as operating on only a single pin or elongated electrical conductor and would be difficult to adapt to a connector having multiple pins. Additionally, many connectors for high frequency cable contain an dielectric material cylinder that protrudes at least the length of the pin. For such connectors, the coiled compression spring would not be able to contact both the pin and the exterior conductor when uncompressed.
Another prior art electrical connector-receptacle arrangement is described in commonly assigned U.S. Pat. No. 4,971,568 entitled "Electrical Connector Attachment for Automatically Shorting Select Conductors Upon Disconnection of Connector" by David V. Cronin issued Nov. 20, 1990. This patent shows a shunt attachment placed on pins of the connector arranged to provide a short circuit across selected pins. Upon insertion into the receptor, the attachment is compressed causing the short circuit to be broken. While this arrangement is an improvement and is useful for connectors having multiple pins, it is planar and, therefore, can not connect conductors separated by an insulating layer of the type commonly employed in coaxial cable connectors. Other commonly assigned patents relating to electrostatic discharge protection include U.S. Pat. No. 5,163,850 entitled "Electrostatic Discharge Protection Devices for Semiconductor Chip Packages," by David V. Cronin, issued Nov. 17, 1992; U.S. Pat. No. 5,164,880 entitled "Electrostatic Discharge Protection Device for a Printed Circuit Board," by David V. Cronin, issued Nov. 17, 1992; and U.S. Pat. No. 5,108,299 entitled "Electrostatic Discharge Devices for Semiconductor Chip Packages," by David V. Cronin, issued Apr. 28, 1992.
Accordingly, it is an object of this invention to provide an electrostatic discharge protection device operates to automatically open a short between selected conductors upon connection to a mating connector.
It is another object of this invention to provide an electrostatic discharge protection device for use with connectors having a plurality of elongate conductors.
It is still another object of the invention to provide an electrostatic discharge protection device which is operable with non-planar conductor arrangements such as those containing dielectric material shields around conductors.
These and other objects of the invention will be obvious and will appear hereinafter.